Mother's blood shows birth defects in fetal DNA

Researchers said Wednesday they were able to sequence the entire genome of a fetus using only a blood sample from the mother, an advance in the effort to find noninvasive ways for expectant parents to determine if their babies will be born with genetic conditions.

The findings, from researchers at Stanford University School of Medicine, reflect intense interest in finding fast, relatively inexpensive and accurate ways to predict genetic conditions without the risks associated with currently available tests. Amniocentesis, for instance, which many couples rely on to obtain some genetic information about the fetus, requires insertion of a needle through the walls of a pregnant woman's abdomen and uterus, and has a small risk of miscarriage. The study was funded by the National Institutes of Health and the Howard Hughes Medical Institute.

The Stanford technique, researchers said, doesn't require DNA from the father, an advantage given that a child's paternity may not be known in as estimated 3% to 10% of births in the U.S., according to sources cited in the Nature paper. "It is not that practical to assume you can get DNA from dad or you even know who dad is,'' said Stephen R. Quake, a professor of applied physics and bioengineering at Stanford and senior author of the study. The findings were published in the July 4 issue of the journal Nature.

The study grew out of a discovery made in the late 1990s that a fetus releases DNA into the mother's blood during pregnancy. A number of companies, including two co-founded by Dr. Quake, are already using molecular counting techniques to measure the presence of elevated amounts of chromosome 21 relative to other chromosomes in a mother's blood to determine if a fetus has Down syndrome, a genetic condition that causes cognitive disabilities. The current study takes the method "and applies it to the whole genome,'' said Dr. Quake.

It will probably take a few more years before such noninvasive whole genome tests are ready for use in the clinic, said Jay A. Shendure, associate professor of genome sciences at the University of Washington, who wasn't involved in the latest research. He was principal investigator in a study published last month in Science Translational Medicine that sequenced the fetal genome using a blood sample from the mother and saliva from the father.